已知sinα+conα=1/5,且π/2≤α≤3π/4,则con2α的值是
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已知sinα+conα=1/5,且π/2≤α≤3π/4,则con2α的值是
已知sinα+conα=1/5,且π/2≤α≤3π/4,则con2α的值是
已知sinα+conα=1/5,且π/2≤α≤3π/4,则con2α的值是
cos2α=(cosα)^2-(sinα)^2;又cosα)^2+(sinα)^2=1sinα+cosα=1/5,两边平方,可以求出2sinα*cosα的值;从而根据π/2≤α≤3π/4,从而可以求得sinα、cosα的值.
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